Orks don’t have enough structure to be called Fascist (They’re really the universes fastest assembling and most violent flash mob) and Chaos is closer to an absolute monarchy than fascism. Humans and space dwarves are probably the closest to fascism.
Tau would be totalarian communism, and the tyranids would just be completely amoral true socialists? Maybe? I honestly don’t know what to even liken them to.
Histamine receptors, especially 3, are more important than people realize.